I want to display only two images in one row.  

Using my code all images are displayed in a single row.

VF Page :

<apex:page standardController="Flat__c" extensions="displayImageExtension">
<style>
img:hover 
{
height: 400px;
width:  400px;
} 
</style>
<apex:repeat value="{!file}" var="p">
<apex:panelGrid columns="2" style="width:100%;" id="theGrid">
<apex:image id="theImage" url="/servlet/servlet.FileDownload?file={!p.Id}" width="100" height="100" />
</apex:panelGrid>
</apex:repeat>
</apex:page>